1. Field of the Invention
The present invention relates to a liquid crystal display device and, particularly, to a transflective liquid crystal display device capable of display in both of a reflective mode and a transmissive mode.
2. Description of the Related Art
Having features of thinness, light weight, and low power consumption, liquid crystal display devices are widely used in portable information equipment such as cellular phones, PDAs (personal digital assistants), and electronic notes and other electronic equipment such as notebook-sized personal computers, monitors, and camcorders. Liquid crystal display devices that are non-emission-type devices and hence require an external light source are generally classified into a transmissive type and a reflective type by the type of the light source. In transmissive type liquid crystal display devices, a backlight having a light-emitting element(s) such as a cold-cathode tube, LEDs, or the like is used as an external light source and light emitted from the backlight is modulated according to a video signal in passing through a liquid crystal panel. In reflective-type liquid crystal display devices, light coming from such a light source as the sun is reflected by a reflector and light returning to a viewer is modulated by a liquid crystal panel according to a video signal.
However, conventionally, transmissive type devices have a problem that a displayed image is blurred in a bright environment and reflective-type devices have a problem that a displayed image becomes dark in a dark environment. To solve these problems, a transflective liquid crystal display device in which each pixel has a reflective portion and a transmissive portion has been proposed recently (JP-A-2000-187220 (page 5 and FIG. 1). In a bright environment, this transflective liquid crystal display device functions as a reflective-type liquid crystal display device and hence can reduce its power consumption. In a dark environment, it functions as a transmissive type liquid crystal display device and hence can provide a bright, high-quality image. As such, this transflective liquid crystal display device is now widely used in cellular phones.
FIG. 4 is a plan view showing one pixel of a common, conventional transflective liquid crystal display device. FIG. 5 is a sectional view taken along line V—V in FIG. 4. FIG. 6 is a sectional view taken along line VI—VI in FIG. 4. The transflective liquid crystal display device has a transmissive portion 112 and a reflective portion 113 in each pixel and is provided with a first substrate 101 and a second substrate 102 that are opposed to each other. Alignment films 109 and 110 are formed at innermost positions with respect to the first substrate 101 and the second substrate 102, respectively. A liquid crystal layer 111 is held between the alignment films 109 and 110.
A color filter 103 and a color filter black matrix (hereinafter abbreviated as “black matrix”) 104 as a light shield member are formed on the liquid-crystal-111-side major surface 101a of the first substrate 101 in prescribed regions corresponding to each pixel. A transparent electrode 105 and the alignment film 109 are formed on the color filter 103 and the black matrix 104. A quarter-wave plate 114, a half-wave plate 115, and a polarizing plate 116 are laid on the outer major surface 101b of the first substrate 101 to form a circularly polarizing plate 120.
On the other hand, as shown in FIG. 5, a reflective electrode 108 that is a metal film is formed on the liquid crystal-layer-111-side major surface 102a of the second substrate 102 with an organic insulating film 106 and a transparent electrode 107 interposed in between. The opening of the reflective electrode 108 is the transmissive portion 112. As shown in FIG. 6, part of the reflective electrode 108 is formed on an asperity portion of the organic insulating film 106 to serve as the reflective portion 113 having a scattering function.
Incident light is interrupted or transmitted on a pixel-by-pixel basis according to a video signal, that is, a voltage applied between the transparent electrode 105 and the transparent electrode 107/reflective electrode 108. A quarter-wave plate 117, a half-wave plate 118, and a polarizing plate 119 are laid on the outer major surface 102b of the second substrate 102 to form another circularly polarizing plate 121.
The conventional transflective liquid crystal display device having the above configuration has a problem that the display quality is low in the reflective mode in which display is performed on ambient light. This is mainly because leakage light coming from portions other than the reflective portion 113, in particular, slant portions 112a on both sides of the transmissive portion 112, is mixed into reflective light from the reflective portion 113. In a manufacturing process of the liquid crystal display device, the alignment films 109 and 110 are subjected to rubbing treatment to align liquid crystal molecules in a particular direction. However, sufficient rubbing treatment cannot be performed in the vicinities of the slant portions 112a located on both sides of the transmissive portion 112, to cause portions having abnormal liquid crystal alignment. Reflective light and transmissive light from these portions are a factor of lowering the contrast ratio, that is, the display quality, of the liquid crystal display device. Further, the reflective electrode 108 has flat portions 112b on both sides of the transmissive portion 112. The flat portions 112b cause specular reflection in the reflective mode, which results in a problem that the display quality is lowered in the reflective mode.